It is proposed to review and classify the slides from breast biopsies of 1000 women performed 15 or more years as cystic disease at that time. These patients will be followed until their death or the development of mammary carcinoma. Correlative studies between the lesions of cystic disease and the development of mammary carcinoma will be undertaken and used to demonstrate how various kinds of cystic disease lesions and epidemiologic factors are associated with the development of mammary carcinoma.